1. Field of the Invention
The invention relates to an antenna comprised of micro-strip antennas and having bi-directional or non-directional characteristic.
2. Description of the Related Art
FIG. 1 is a perspective view illustrating a conventional antenna comprised of micro-strip antennas and having bi-directional or non-directional characteristic.
As illustrated in FIG. 1, the conventional antenna 102 is comprised of a first micro-strip antenna 104, a second micro-strip antenna 106 spaced away from and facing the first micro-strip antenna 104, a ground plate 108 located between the first and second micro-strip antennas 104 and 106, a first dielectric plate 110a composed of insulating material and sandwiched between the first micro-strip antenna 104 and the ground plate 108, a second dielectric plate 110b composed of insulating material and sandwiched between the second micro-strip antenna 106 and the ground plate 108, and an electric power distributor 112 for feeding electric power to the first and second micro-strip antennas 104 and 106.
A first micro-strip line 114 is formed on a surface of the first dielectric plate 110a and is connected to the first micro-strip antenna 104, and a second micro-strip line 116 is formed on a surface of the second dielectric plate 110b and is connected to the second micro-strip antenna 106. Electric power supplied to a feeding terminal 118 is distributed by the electric power distributor 112 to the first and second micro-strip antennas 104 and 106 through the first and second micro-strip lines 114 and 116, respectively.
However, the antenna 102 is accompanied with a problem that since the first and second micro-strip antennas 104 and 106 are positioned at opposite sides of the ground plate 108, the electric power distributor 112 for feeding electric power to the first and second micro-strip antennas 104 and 106 has to be three-dimensional. Specifically, the electric power distributor 112 has to have a width equal to or greater than a total width of the first and second dielectric plates 110a and 110b. As a result, the antenna 102 cannot avoid being larger in size due to the three-dimensional distributor 112.
Japanese Unexamined Patent Publication No. 6-120729 having been published on Apr. 28, 1994 has suggested an antenna comprised of a first dielectric plate, a second dielectric plate adhered to the first dielectric plate, a first planar electrical conductor formed on a surface of the first dielectric plate, and a second planar electrical conductor formed on a surface of the second dielectric plate.
The antenna suggested in the above-mentioned Publication is accompanied with the same problem as that of the antenna illustrated in FIG. 1. Namely, since the first and second planar electrical conductors are positioned at opposite sides of the dielectric plates, an electric power distributor for feeding electric power to the first and second planar electrical conductors has to be three-dimensional, due to which the antenna cannot avoid to be larger in size.
Japanese Unexamined Patent Publication No. 7-46028 having been published on Feb. 14, 1995 has suggested an antenna comprised of a dielectric plate, and radiation slots formed on opposite surfaces of the dielectric plate.
Since the radiation slots are formed at opposite surfaces of the dielectric plate, the antenna suggested in the above-identified Publication is accompanied with a problem that an electric power distributor for feeding electric power to the radiation slots has to be three-dimensional, due to which the antenna cannot avoid to be larger in size.